The specific reaction of a particular protein with another particular protein is well known, for example, the development within animals of a specific antibody to combat a particular antigen is well known. This specificity of one protein for another has been utilized in affinity chromatography to separate a specific protein which was present in a particular solution.
The selective reaction between two compounds exists for other compounds besides proteins, for example, enzymes and poly and monosaccharides selectively react with specific compounds, and is identified herein as an immunochemical reaction.
Affinity chromatographic materials, e.g., column packing objects, are prepared from hydrophilic polymeric surfaces which, by their polar nature, have reactive sites to which a protein reactive compound can be attached. The hydrophilic nature of the substrate is not affected by the attachment of the protein.
A protein molecule such as an antibody or antigen in a buffer solution has a net surface charge magnitude and polarity which depends on the isoelectric point of the protein and the composition of the buffer. This surface charge changes as a result of antibody-antigen reaction. Although the net change in electrical charge is of a magnitude to be detected, immobilization of a protein on a hydrophilic membrane is unsatisfactory because the ionic action of water on the polar groups of the hydrophilic substrate is so great that it masks the slight electrical potential change induced by the immunochemical reaction.